By Jennifer Piacenti The Bills are the Super Bowl favorites at SI Sportsbook halfway through the season, ahead of the NFC-leading Eagles. We’re at the midway point of the season and it’s time to check in on the Super Bowl futures at SI Sportsbook to try to find some value. This list looks very different from the preseason, though the Bills remain the favorites to win the Super Bowl. They entered the season with 6-1 odds, and those who took them early probably feel good about their bet. The biggest riser is the undefeated Eagles. The 8-0 Eagles have simply looked unstoppable. They are complete …